Food Additives & Contaminants
ISSN: 0265-203X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/tfac19
‘Threshold effect’ of increasing tocopherol ingestion upon the microsomal epoxide hydrolase activity of rat liver J. Mounie , H. Goudonnet , J. Magdalou , A. Escousse , G. Siest & R‐C. Truchot To cite this article: J. Mounie , H. Goudonnet , J. Magdalou , A. Escousse , G. Siest & R‐C. Truchot (1990) ‘Threshold effect’ of increasing tocopherol ingestion upon the microsomal epoxide hydrolase activity of rat liver, Food Additives & Contaminants, 7:S1, S106-S107, DOI: 10.1080/02652039009373859 To link to this article: http://dx.doi.org/10.1080/02652039009373859
Published online: 10 Jan 2009.
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tfac19 Download by: [Monash University Library]
Date: 20 November 2015, At: 05:33
FOOD ADDITIVES AND CONTAMINANTS, 1990, VOL. 7, SUPPLEMENT NO. 1, S106-S107
'Threshold effect' of increasing tocopherol ingestion upon the microsomal epoxide hydrolase activity of rat liver J. MOUNIE, H. GOUDONNET, J. MAGDALOU†, A. ESCOUSSE, G. SIEST† and R-C. TRUCHOT
Downloaded by [Monash University Library] at 05:33 20 November 2015
Formation 'Biochimie Pharmacologique' Université de Bourgogne, 7 Bvd Jeanne d'Arc, 21 033 Dijon, France, and †Centre du Médicament, U R A CNRS 597, Université de Nancy, 30 rue Lionnois, 54 000 Nancy, France
Introduction
The conversion of the antioxidant effect of tocopherol on lipids to a prooxidant effect has been largely reviewed and investigated by Cillard and Cillard (1980a,b) and Cillard et al. (1980). This pro-oxidant effect depends on two factors: The concentration of tocopherol ( ^ 5 x l 0 ~ 3 m o l tocopherol/mol linoleic acid); The nature of the solvent, since this effect occurs more easily in aqueous systems (Cillard et al. 1980). In an attempt to measure the tocopherol pro-oxidant effect we studied the influence of increased levels of tocopherol upon hepatic microsomal epoxide hydrase (EH) activity. Methods
Thirty-two male Wistar rats weighing 80-100 g (at the beginning of the experiment), acclimatized with a standard diet for one week, were fed a semisynthetic diet whose composition has been previously described (Mounie et al. 1986). In order to control the tocopherol ingestion the lipid composition (2%) was: diolein, linolenic acid, linoleic acid (1:1:1, ww); and the vitamin mixture was prepared without vitamin E. After 2 weeks of this diet, the diet was supplemented with increasing amounts of DL-a-tocopherol: 0, 3, 100, 160 mg/kg per day (gastric intubation) (diets: A, B, C, D) for 3 weeks. The animals were sacrificed and the EH activity was determined in microsomes with the benzo(a)pyrene-4,5-oxide as substrate. Microsomal tocopherol content was determined by a HPLC fluorimetric method (Exc 290 nm, Em 325 nm) with tocol (synthesized in our laboratory) as internal standard (0-5 ngjml). Results With the above treatment, the tocopherol concentration in liver microsomes increased from 1-3(A) to respectively 2-4(B), 20(C), 38(D) nmol tocopherol/mmol O265-2O3X/9O $3.00© 1990 Taylor & Francis Ltd.
S107
Tocopherol and microsomal EH activity (a)
I
5000 -(000
(b)
3000
ntnol ZmmoV Ptosphollpkb
"1
2000
nraoV /mln/mg
1000 0
Downloaded by [Monash University Library] at 05:33 20 November 2015
A.
B
C.
ANIMALS SERIES
A
B
C
ANIMALS SERIES
Figure 1. Evidence of a threshold effect of tocopherol ingestion: (a) tocopherol microsomic concentration, (b) microsomic epoxide hydrase.
phosphatidylcholine (see figure 1 a). By contrast the microsomal EH activity was not changed, except with the highest tocopherol dose (160 mg/kg per day) for which this activity was strongly increased (up to four times) (figure Ib). Conclusions
The effect of the largest tocopherol dose reveals a threshold effect upon the microsomal EH activity, suggesting the formation of a large amount of epoxidecontaining compounds into the microsomal membranes. Bruice (1988) proposed that alkene epoxidation in biological membranes can result from oxygen transfer from acyl hydroperoxides to metal III porphyrins. Even if the direct prooxidant effect of tocopherol has never been described in vivo, an excess of tocopherol could activate, in our liminar nutritional conditions, the process of alkene epoxidation. References BRUICE, T. C., 1988, The mechanisms of oxygen transfer from acyl and alkyl hydroperoxides to metal (III) porphyrins and the epoxidation of alkenes by the resultant hypervalent metal-oxo porphyrin products. Aldrichimica Acta, 21, 87-94. CILLARD, J., and CILLARD, P., 1980a, Etude de l'effet prooxygène de l'α-tocophérol sur les acides gras essentiels en milieu aqueux. Annales de Nutrition et Alimentation, 34, 579-592. CILLARD, J., and CILLARD, P., 1980b, Behavior of alpha, gamma, and delta tocopherols with linoleic acid in aqueous media. Journal of the American Oil Chemists Society, 57, 39-42. CILLARD, J., CILLARD, P., and CORMIER, M., 1980, Effect of experimentais factors on the prooxidant behavior of α-tocopherol. Journal of the American Oil Chemists Society, 57, 257-261. MOUNIE, J., FAYE, B., MAGDALOU, J., GOUDONNET, H., TRUCHOT, R., and SIEST, G., 1986, Modulation
of UDP-glucuronosyltransferase activity in rats by dietary lipids. Journal of Nutrition, 116, 2034-2043.
ISSN: 0265-203X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/tfac19
‘Threshold effect’ of increasing tocopherol ingestion upon the microsomal epoxide hydrolase activity of rat liver J. Mounie , H. Goudonnet , J. Magdalou , A. Escousse , G. Siest & R‐C. Truchot To cite this article: J. Mounie , H. Goudonnet , J. Magdalou , A. Escousse , G. Siest & R‐C. Truchot (1990) ‘Threshold effect’ of increasing tocopherol ingestion upon the microsomal epoxide hydrolase activity of rat liver, Food Additives & Contaminants, 7:S1, S106-S107, DOI: 10.1080/02652039009373859 To link to this article: http://dx.doi.org/10.1080/02652039009373859
Published online: 10 Jan 2009.
Submit your article to this journal
Article views: 5
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tfac19 Download by: [Monash University Library]
Date: 20 November 2015, At: 05:33
FOOD ADDITIVES AND CONTAMINANTS, 1990, VOL. 7, SUPPLEMENT NO. 1, S106-S107
'Threshold effect' of increasing tocopherol ingestion upon the microsomal epoxide hydrolase activity of rat liver J. MOUNIE, H. GOUDONNET, J. MAGDALOU†, A. ESCOUSSE, G. SIEST† and R-C. TRUCHOT
Downloaded by [Monash University Library] at 05:33 20 November 2015
Formation 'Biochimie Pharmacologique' Université de Bourgogne, 7 Bvd Jeanne d'Arc, 21 033 Dijon, France, and †Centre du Médicament, U R A CNRS 597, Université de Nancy, 30 rue Lionnois, 54 000 Nancy, France
Introduction
The conversion of the antioxidant effect of tocopherol on lipids to a prooxidant effect has been largely reviewed and investigated by Cillard and Cillard (1980a,b) and Cillard et al. (1980). This pro-oxidant effect depends on two factors: The concentration of tocopherol ( ^ 5 x l 0 ~ 3 m o l tocopherol/mol linoleic acid); The nature of the solvent, since this effect occurs more easily in aqueous systems (Cillard et al. 1980). In an attempt to measure the tocopherol pro-oxidant effect we studied the influence of increased levels of tocopherol upon hepatic microsomal epoxide hydrase (EH) activity. Methods
Thirty-two male Wistar rats weighing 80-100 g (at the beginning of the experiment), acclimatized with a standard diet for one week, were fed a semisynthetic diet whose composition has been previously described (Mounie et al. 1986). In order to control the tocopherol ingestion the lipid composition (2%) was: diolein, linolenic acid, linoleic acid (1:1:1, ww); and the vitamin mixture was prepared without vitamin E. After 2 weeks of this diet, the diet was supplemented with increasing amounts of DL-a-tocopherol: 0, 3, 100, 160 mg/kg per day (gastric intubation) (diets: A, B, C, D) for 3 weeks. The animals were sacrificed and the EH activity was determined in microsomes with the benzo(a)pyrene-4,5-oxide as substrate. Microsomal tocopherol content was determined by a HPLC fluorimetric method (Exc 290 nm, Em 325 nm) with tocol (synthesized in our laboratory) as internal standard (0-5 ngjml). Results With the above treatment, the tocopherol concentration in liver microsomes increased from 1-3(A) to respectively 2-4(B), 20(C), 38(D) nmol tocopherol/mmol O265-2O3X/9O $3.00© 1990 Taylor & Francis Ltd.
S107
Tocopherol and microsomal EH activity (a)
I
5000 -(000
(b)
3000
ntnol ZmmoV Ptosphollpkb
"1
2000
nraoV /mln/mg
1000 0
Downloaded by [Monash University Library] at 05:33 20 November 2015
A.
B
C.
ANIMALS SERIES
A
B
C
ANIMALS SERIES
Figure 1. Evidence of a threshold effect of tocopherol ingestion: (a) tocopherol microsomic concentration, (b) microsomic epoxide hydrase.
phosphatidylcholine (see figure 1 a). By contrast the microsomal EH activity was not changed, except with the highest tocopherol dose (160 mg/kg per day) for which this activity was strongly increased (up to four times) (figure Ib). Conclusions
The effect of the largest tocopherol dose reveals a threshold effect upon the microsomal EH activity, suggesting the formation of a large amount of epoxidecontaining compounds into the microsomal membranes. Bruice (1988) proposed that alkene epoxidation in biological membranes can result from oxygen transfer from acyl hydroperoxides to metal III porphyrins. Even if the direct prooxidant effect of tocopherol has never been described in vivo, an excess of tocopherol could activate, in our liminar nutritional conditions, the process of alkene epoxidation. References BRUICE, T. C., 1988, The mechanisms of oxygen transfer from acyl and alkyl hydroperoxides to metal (III) porphyrins and the epoxidation of alkenes by the resultant hypervalent metal-oxo porphyrin products. Aldrichimica Acta, 21, 87-94. CILLARD, J., and CILLARD, P., 1980a, Etude de l'effet prooxygène de l'α-tocophérol sur les acides gras essentiels en milieu aqueux. Annales de Nutrition et Alimentation, 34, 579-592. CILLARD, J., and CILLARD, P., 1980b, Behavior of alpha, gamma, and delta tocopherols with linoleic acid in aqueous media. Journal of the American Oil Chemists Society, 57, 39-42. CILLARD, J., CILLARD, P., and CORMIER, M., 1980, Effect of experimentais factors on the prooxidant behavior of α-tocopherol. Journal of the American Oil Chemists Society, 57, 257-261. MOUNIE, J., FAYE, B., MAGDALOU, J., GOUDONNET, H., TRUCHOT, R., and SIEST, G., 1986, Modulation
of UDP-glucuronosyltransferase activity in rats by dietary lipids. Journal of Nutrition, 116, 2034-2043.
